You might want to explain why you think saying anything is necessary. Any particular things they say or do that make you feel they think you are stupid? Be specific.
Frankly, and I know you asked for "creative" responses, but a lot of the time when it comes to being made to feel as though others think you are stupid, a direct response can be the best.
"Hey, you know what? I'm not stupid ya know!" might take people off guard, but it also tends to cause reasonable people to stop and think about what they did or said that would cause you to think you needed to say it.
So what about unreasonable people?
Well, they can't be reasoned with anyway, so why bother. I choose to be blunt in these situations because the bluntness reveals whether they are reasonable or unreasonable. If they are reasonable, it will usually result in intelligent conversation and hopefully a little enlightenment in them. If they are unreasonable, I'll usually get a response like, "Oh lighten up! Stop taking yourself so seriously!" and trying to enlighten anybody like that is just a waste of time. Leave them be and let them flounder in their ignorance.
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I'm not likely to be around much longer. As before when I first signed up here years ago, I'm finding that after a long hiatus, and after only a few days back on here, I'm spending way too much time here again already. So I'm requesting my account be locked, banned or whatever. It's just time. Until then, well, I dunno...